The present invention relates to a copier, facsimile apparatus or similar image forming apparatus and, more particularly, to a sheet feed device for such an image forming apparatus and having a plurality of substantially horizontal sheet feed portions arranged serially in an intended direction of sheet transport.
It has been customary with a family of image forming apparatuses mentioned above to mount a plurality of cassettes on the apparatus body for accommodating sheets of different sizes and different kinds. A front loading type sheet feed device, or sheet feeder, is spreading in which trays are arranged one above the other in multiple stages for a space saving purpose. The problem with the conventional front loading type sheet feeder is that since each sheet feed stage is loaded with a single kind of sheets, trays assigned to sheets of small sizes, e.g., A4 and B5 are of the same size as trays assigned to sheets of large sizes, e.g., A3 and B4. As a result, the sheet feeder is bulky. Moreover, since the height of such a sheet feeder is limited to promote easy manipulation, the number of sheets which can be accommodated in the sheet feeder is limited.
In the light of this, the sheet feed stages may include one having two sheet storing portions each being loaded with sheets of particular size, as disclosed in Japanese Patent Laid-Open Publication No. 204237/1990 by way of example. Alternatively, use may be made of a cassette capable of storing two kinds of sheets and provided with feeding means at opposite sides thereof with respect to a direction of sheet feed, as taught in, e.g., Japanese Patent Laid-Open Publication No. 192032/1991. These schemes each use either a sheet feed stage or a cassette for feeding two kinds of sheets in order to reduce the number of sheet feed stages or the number of cassettes. However, each of the two storing portions constituting the sheet feed stage or the cassette has respective transport path extending to an image forming section, as in the plural sheet feed stage scheme or the plural cassette scheme. In such a configuration, the transport paths need an additional space and, therefore, increase the overall size of the sheet feeder. In addition, the double path configuration specializes and complicates the sheet feeder.
There has been proposed a sheet feeder including a sheet feed stage having two sheet storing portions which are capable of storing sheets of two small sizes. In this sheet feeder, the sheets are selectively fed out from the two sheet storing portions. This is successful in effectively using the space heretofore wasted, inclusive of the transport paths, and, in increasing the capacity of the sheet feeder. To adapt the sheet feeder to the front loading arrangement as well, the two sheet storing portions are arranged serially in the direction of sheet feed, and each is provided with respective sheet feeding and separating means. A sheet paid out from the rear storing portion is transported to the sheet feeding and separating means associated with the front storing portion. As a result, the sheets from the two storing portions are fed out over a common path. However, since the sheets from both of the two storing portions arrive at the sheet feeding and separating means adjoining the front storing portion, a problem particular to this kind of sheet feeder arises. Specifically, the sheets from the two storing portions are apt to overlap at the sheet feeding and separating means or to jam the path terminating thereat.